1. Field of the Invention
The present invention relates to a lens barrel suitable for use with a zoom lens system such as that proposed by the assignee of the present application in U.S. patent application Ser. No. 09/534,307 (Japanese Patent Application No. Hei 11-79572).
2. Description of the Related Art
In a zoom lens system of the prior art, there are contradictory demands for a high zoom ratio and miniaturization. For example, in a two-lens-group zoom lens system which can be miniaturized, if the paths of the lens groups thereof (hereinafter, lens-group-moving paths) are determined (i.e., solutions for lens-group-moving paths) so that the zoom ratio becomes high, interference of the lens groups occurs on the telephoto side, or interference of a lens group and the image plane occurs on the wide-angle side. On the other hand, in a three-lens-group zoom lens system, the zoom ratio thereof can be made higher than that of a two-lens-group zoom lens system; however, miniaturization is difficult. Furthermore, if an attempt is made to obtain a higher zoom ratio, and if the power of these three lens groups is determined accordingly, precision on the operations of the system cannot be obtained due to the mechanical structure thereof.
The assignee of the present application has proposed an unprecedented zoom lens system that meets the contradictory demands of high zoom ratio and miniaturization (U.S. patent application Ser. No. 09/534,307). This zoom lens system has the following characteristics: it includes a plurality of movable lens groups for varying the focal length; at least one of the lens groups is a switching lens group which includes two sub-lens groups, one of the sub-lens groups being a movable sub-lens group that can be selectively positioned at either one movement extremities in the optical axis direction with respect to the other sub-lens group; the movable sub-lens group of the switching lens group is positioned at an extremity of a short-focal-length zooming range, from the short focal length extremity to an intermediate focal length, and at the opposite extremity of a long-focal-length zooming range, from the intermediate focal length to a long focal length extremity; and zoom paths of the switching lens group and the other lens groups are discontinuous at the intermediate focal length and are defined to focus on a predetermined image plane corresponding to the position of the movable sub-lens group. There may be one or more intermediate focal lengths.
Accordingly, it is an object of the present invention to provide a lens barrel suitable for use with a zoom lens system that includes the switching lens group as described above. It is another object of the present invention to provide a lens barrel for use with the switching lens group which is preferably used when the switching lens group forms a focus lens group which advances or retreats in the optical axis direction regardless of the zooming ranges.
In order to achieve the above-mentioned objects, a lens barrel having a zoom lens system is provided, the zoom lens system including a plurality of variable power lens groups which are movable in an optical axis direction for varying the focal length of the zoom lens system; wherein at least one of the variable power lens groups includes a switching lens group having two sub-lens groups, one of the sub-lens groups constituting a movable sub-lens group that is selectively positioned at one of two movement extremities, in the optical axis direction, with respect to the other of the sub-lens groups; the movable sub-lens group of the switching lens group is positioned at one of the movement extremities in a short-focal-length side zooming range from a short focal length extremity to an intermediate focal length, and at the other of the movement extremities in a long-focal-length side zooming range from the intermediate focal length to a long-focal-length extremity; zoom paths of the two sub-lens groups of the switching lens group and the other of the variable power lens groups are discontinuous at the intermediate focal length and are defined so that the zoom lens system forms an image on a predetermined image plane in accordance with a position of the movable sub-lens group; and the switching lens group is a focusing lens group which integrally advances and retreats in the optical axis direction regardless of the zooming range. The lens barrel includes a first sub-lens group frame for supporting the one of the sub-lens groups; a second sub-lens group frame for supporting the other of the sub-lens groups; a switching lens group frame for supporting the first sub-lens group frame and the second sub-lens group frame in a manner that allows the sub-lens groups to move in the optical axis direction; a shift mechanism for selectively moving the first sub-lens group frame and the second sub-lens group frame in the switching lens group frame to a mutually close position and to a mutually distant position, the mutually close position and the mutually distant position corresponding to one and the other of the movement extremities, respectively; and a switching lens group frame moving mechanism for moving the switching lens group frame with the other of the variable power lens groups along a predetermined path to vary the focal length. Combined movement of the shift mechanism and the switching lens group frame moving mechanism provides the zoom paths of the two sub-lens groups of the switching lens group.
Preferably, the shift mechanism also serves as a focusing mechanism that causes the first and second sub-lens group frames, when in one of the mutually close position and the mutually distant position, to integrally move forwardly or rearwardly in the optical axis direction.
In an embodiment, the shift mechanism and the switching lens group frame moving mechanism move the switching lens group frame and the second sub-lens group frame so that the zoom path of the second sub-lens group frame is not discontinuous between the short-focal-length side zooming range and the long-focal-length side zooming range, which extend on both sides of the intermediate focal length.
In an embodiment, stop positions at which the switching lens group frame, the first and second sub-lens group frames come to a stop upon photographic operation are determined in a stepwise manner along the zoom path.
Preferably, the shift mechanism includes an actuator ring rotatably supported in the switching lens group frame, the actuator ring providing relative rotation between the first sub-lens group frame and the second sub-lens group frame; and a shift cam mechanism provided on opposed surfaces of the first sub-lens group frame and the second sub-lens group frame, the shift cam mechanism causing the first and second lens group frames to come to the mutually close position and to the mutually distant position, in the optical axis direction, in accordance with the relative rotation between the first lens group frame and the second lens group frame.
Preferably, the switching lens group frame moving mechanism includes a zooming motor, and a rotatable cam ring which is rotatably driven by the zoom motor, the cam ring including at least one cam groove on an inner surface thereof for moving the switching lens group frame in the optical axis direction when the cam ring is rotated.
Preferably, the cam ring further includes another cam groove on the inner surface thereof for moving a variable power lens group frame, which differs from the switching lens group frame, in accordance with the rotation of the cam ring.
According to another aspect of the present invention, a lens barrel having a zoom lens system is provided, the zoom lens system including a plurality of variable power lens groups which are movable in an optical axis direction for varying the focal length of the zoom lens system, at least one of the variable power lens groups including a switching lens group having two sub-lens groups which are optically operable in a mutually close position and in a mutually distant position in the optical axis direction, the lens barrel includes a first sub-lens group frame for supporting one of the sub-lens groups; a second sub-lens group frame for supporting the other of the sub-lens groups; a switching lens group frame for supporting the first sub-lens group frame and the second sub-lens group frame in a manner that allows the sub-lens groups to move in the optical axis direction; a shift mechanism for selectively moving the first sub-lens group frame and the second sub-lens group frame in the switching lens group frame to the mutually close position and to the mutually distant position; and a switching lens group frame moving mechanism for moving the switching lens group frame with the other of the variable power lens groups along a predetermined path to vary the focal length. Combined movement of the shift mechanism and the switching lens group frame moving mechanism provides a zoom path for the two sub-lens groups of the switching lens group.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-288549 (filed on Sep. 22, 2000) which is expressly incorporated herein in its entirety.